如何在C++中实现类组合？

#include<iostream>

class Engine {
public:
    void start() {
        std::cout << "Engine started."<< std::endl;
    }
};

class Car {
private:
    Engine engine;

public:
    void start() {
        engine.start();
    }
};

int main() {
    Car car;
    car.start();

    return 0;
}